The invention relates to a die plate for the rotor of a rotary tablet press comprising a plurality of die holes, with dies provided therein, arranged distributed in the circumferential direction of the die plate, and radial bores, running between every two adjacent die holes, in each of which a fastening device is disposed for fastening the dies. Known fastening devices for fastening dies have a conical bolt and a set screw assigned to this. The conical bolts of the fastening devices are each inserted into a radial bore of the die plate. Following that, the set screws are screwed into the radial bores, wherein the conical bolts are in each case pressed against dies disposed adjacent to the radial bores.
These known fastening devices have a few disadvantages. For example, the set screws are screwed from the circumferential outside of the die plate into the internal thread formed in the radial bores, where they press the conical bolts located further inward in the radial direction against the dies. This design requires significant construction space in the radial direction, whereby the necessary outer diameter of the die plate and thus the dimensions of the rotary tablet press increase undesirably. Furthermore, threaded bores must be provided in the die plate for the set screws, which is costly. In the case of damage to the thread, they cannot be exchanged. Specifically with the high chrome tools frequently used here, the threads are prone to increased wear, particularly to seizing. Defective threads, in turn, increase the risk that dies can loosen from the plate which can lead to damaging the machine. Furthermore, the radial threaded bores, into which the set screws are screwed, cannot be cleaned in a satisfactory manner. In addition to this, there is the fact that the dies are held by the conical bolts in each case only at two sections of their outer surface at the dies. In adverse cases, this can lead to a tilting or tipping of the dies. This in turn, leads to inaccuracies of the fit, and thus to an increased wear of the dies, and to the press punches interacting with them. Beyond that, the known fastening devices exert strong forces on the dies in the radial direction. This is disadvantageous for maintaining the positioning of the dies, and can lead to a deformation of the dies. As a result, the press punches of the rotary press can, in turn, rub against the inner wall of the dies, leading to increased wear.
Starting from the described prior art as a background, the object of the invention is to provide a die plate of the initially named type which is structurally more compact, more robust and which makes possible a uniform and precise fastening of the dies in a wear resistant manner.
The invention solves this objective by the subject matter of claim 1. Advantageous embodiments are found in the dependent claims, the description and the drawings.
The object of the invention is solved for a die plate of the initially named type in that at least one fastening device comprises two clamping elements disposed opposite each other in a radial bore, and one tensioning device, wherein the clamping elements can be tensioned against each other in the radial direction using the tensioning device, wherein the clamping elements are pressed against the dies adjacent to the radial bore.
Naturally, all of the fastening devices of the die plate are designed in the inventive manner. The die plate can be designed to be integrally formed or consist of die segments. The die plate is designed to have a circular ring shape, for example. It is part of a rotor of a rotary table press and can be driven rotatingly together with the rotor about a typically vertical axis of rotation. A plurality of holes for receiving dies, with dies disposed therein, are located in the die plate axis parallel to the axis of rotation of the die plate and of the rotor. A cylindrical bore, for example, running in each case between two adjacent die holes, runs radially to the axis of rotation of the die plate and the rotor of the press. An inventive fastening device having clamping elements is disposed in at least one, for example, in all of these radial bores. The clamping elements located respectively across from each other in a radial bore form a clamping element pair. At least one, preferably both clamping elements of a clamping element pair are already inserted into the respective radial bores before the insertion of the dies into the die holes.
The radial bores each create a connection between each of two adjacent die holes so that the clamping elements of a clamping element pair, with dies inserted into the die holes, can come into contact with both dies adjacent to the radial bore or adjoining the radial bore. Clamping elements opposite each other in a radial bore are pressed according to the invention during tensioning by means of the tensioning device assigned to them, respectively, from opposite sides against the dies adjoining to the radial bores. A radially inner clamping element of a clamping pair is located before and also possibly after tensioning at least in sections within the die hole or a center vertical axis of the die hole, as viewed in a radial direction. The other, radially outer clamping element of the clamping element pair is located correspondingly before and also possibly after tensioning at least in sections outside of the die hole or a center vertical axis of die hole, as viewed in a radial direction. Naturally, the clamping elements must not come directly into contact with the dies during tensioning. It is also conceivable that a force transfer means, for example an elastic intermediate layer, is disposed between the clamping elements and the dies, which transfers the compressive force generated during tensioning the clamping elements onto the dies.
According to the invention, the dies are each held at four sections by the clamping elements disposed particularly on both sides of the dies. Thereby, tipping or other misalignment of the dies is reliably avoided, and retaining forces are more uniformly introduced. Furthermore, by pressing the clamping elements, disposed in a radial bore, from opposite sides against the dies, the dies are fastened without radial forces acting on the dies. Thereby, twisting or misalignment of the dies is reliably excluded. Furthermore, in particular, the inventive radial bores in the die plate do not themselves have a thread. In this way, the clamping elements are freely movable in the radial bore and can be placed against the respective die without twisting. Furthermore, the formation of the radial bore without threads simplifies the production. Also, steps within the bores, which are required in the prior art for diameter expansions of the radial bores, are not necessary according to the invention. Rather, the radial bores can, in a simple manner, be cylindrical bores. Because the radial bores do not require a thread, cleaning is also simplified. Furthermore, in operation the radial bores are subjected to practically no wear, so that damage, and with it also a possibly required exchange, can be avoided. Finally, according to the invention, a reduction of the required construction space is achieved particularly in the radial direction, in particular a reduction of the length of the radial bores. Therefore, the die plate in turn can also be constructed more compactly.
For a further improved fastening of the dies, the clamping elements can each have two clamping surfaces, with which they are pressed against the dies adjacent to the radial bore. Thereby, force is introduced more uniformly. A further more uniform introduction of force, and with it an optimized die fastening is attained if according to a further design the clamping surfaces of the opposite clamping elements taper at least in sections in the direction of the respective other clamping element. The clamping surfaces can taper, in particular, conically. With this design, in the course of tensioning, an automatic self centering of the clamping cone occurs in the radial bores, so that twisting and with it misalignment of the dies is reliably avoided.
According to a further design, a first of the two clamping elements can be designed sleeve-shaped having an internal thread, and the tensioning device has a dowel pin having an external thread, wherein the clamping elements can be tensioned against each other in the radial direction by screwing the dowel pin into the internal thread of the first clamping element. A particularly simple tensioning of the clamping elements and with this, fastening of the dies, is attained in this manner. The radial bore can be accessible particularly from the circumferential side of the die plate. A screwing of the clamping elements by the set screw from the outside is then possible in a particularly simple manner. The sleeve-shaped first clamping element having an internal thread can in particular be the radially inward located clamping element of the two clamping elements. It can then be further provided that the second clamping element is also designed sleeve-shaped, wherein the dowel pin is guided through the second clamping element and can be screwed with its end protruding out of the second clamping element into the first clamping element, and the dowel pin has a stop on which the second clamping element is supported during tensioning of the clamping elements. Here, the second clamping element has, in particular, no internal thread. Rather, the set screw can simply be inserted through this clamping element. The second clamping element is supported against the stop surface which is formed as a flange-like expansion at the screw head, for example.
According to a further design, a transfer device can be provided that takes the second clamping element along with it during removal of the dowel pin from the radial bore. The transfer device can comprise a locking ring disposed at the dowel pin, wherein the second clamping element is held between the stop and the locking ring. The locking ring can be integrally connected to the dowel pin, for example. It ensures that the second clamping element, held between the stop and the locking ring, during withdrawal from the radial bore, particularly unscrewing out of the first clamping element, is also taken along and likewise removed. This simplifies maintenance of the fastening device. Alternatively, it is also possible that the second clamping element and the dowel pin are formed integrally.
According to a further design it can be provided that the first clamping element and the dowel pin are formed integrally, and the second clamping element is formed sleeve-like, wherein the dowel pin is guided through the second clamping element so that the dowel pin extends with one end out of the second clamping element and that the dowel pin has an external thread at least in one area of its end extending out of the second clamping element, upon which a screw nut can be screwed for tensioning the clamping elements against each other.
For a particular uniform and defined the fastening of the dies, the clamping elements during tensioning can engage in annular grooves, which are formed on the outer surfaces of the dies adjacent to the radial bore. The dies can, in a known manner, comprise a cylindrical shape, for example. The annular grooves can, also in a known manner, be designed as (partially) circular in cross-section, for example. Naturally, all dies can have such an annular groove. It can be further provided that at least the die holes for dies that are adjacent to the radial bores receiving the clamping elements, have a collar as an abutment surface for the dies. Using such a collar guarantees a secure hold of the dies and a defined position in the holes before tightening the clamping elements. Naturally, all die holes can in turn have such a collar.
It can be further provided that the center axis of the radial bore receiving the clamping elements is disposed offset with respect to the annular grooves of the dies adjacent to the radial bore, such that the dies during tensioning of the clamping elements against each other are pressed against the respective collar of their die hole. The center axes of the radial bores can be disposed offset with respect to the annular grooves particularly in the axial direction of the die plate, for example to the center axes of the annular grooves that are partially circular in cross section. In this manner, during tensioning of the clamping elements, the dies are pressed against the collar. As a result, a precise and defined fastening of all dies in the receiving hole assigned to each is achieved.
According to a further design, means for the lock against rotation can be provided which prevent a rotation at least of one clamping element in the radial bore. The means for the lock against rotation comprise a projection formed on the clamping element or the radial bore, and a groove, running in the insertion direction of the clamping element in the radial bore, formed on the respectively other clamping element or radial bore, wherein the projection engages in the groove so that a rotation of the clamping element in the radial bore is prevented. In particular, due to the lock against rotation, only the rotation of a first clamping element, namely, for example, the clamping element formed sleeve-shaped and provided with an internal thread, is prevented, so that the dowel pin can be screwed into the first clamping element. The projection can be formed pin-shaped, for example.
Furthermore, the invention relates to a rotary tablet press comprising a rotor that can be driven rotatingly about an axis of rotation, particularly a vertical axis of rotation, that has an inventive die plate and comprises upper and lower punches assigned to the die holes of the die plate, running synchronously with the die plate.